Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, a display apparatus, and a control method for a display apparatus.
Description of the Related Art
In recent years, imaging apparatuses capable of capturing high-dynamic range images (HDR images) have been proposed. In addition, various types of formats have been proposed as data formats for HDR images.
One method of recording an HDR image involves dividing an HDR image into a base image and a tone map and recording the base image and the tone map (WO 2005/104035 and Japanese Patent Application Laid-open No. 2011-193511). In other words, one HDR image format is a format that uses a base image and a tone map. Abase image is a down-sampled (gradation-compressed) image of an HDR image and is an image of around 8-bit gradations. A tone map is information representing a correspondence relationship between a gradation value of a base image and a gradation value of an HDR image. An HDR image can be obtained by converting a gradation value of a base image into a gradation value of an HDR image using a tone map.
In addition, HDR image formats include the ACES standard. The ACES standard is a motion picture standard set forth by the Society of Motion Picture and Television Engineers. The ACES standard is a format in which each color of an HDR image is expressed as a 16-bit floating point.
With an HDR image, actual colors and brightness can be faithfully reproduced.
However, displaying an image that faithfully reproduces actual colors and brightness requires a display apparatus (HDR monitor) compatible with an HDR image format. A maximum value of brightness that can be displayed by existing display apparatuses (existing monitors) is around 103 [cd/m2] and is significantly lower than a maximum value of brightness that occurs in nature. For example, the brightness of sunlight is 109 [cd/m2] and is significantly higher than the maximum value of brightness that can be displayed by existing monitors. As described above, a dynamic range in the natural world is wider than a dynamic range of an image that can be displayed by existing monitors. Therefore, in order to display an image that faithfully reproduces actual colors and brightness, higher brightness than existing monitors must be displayed in a high-brightness region of the HDR image using an HDR monitor capable of displaying images with a wider dynamic range than existing monitors.
A display apparatus may sometimes display an image in which a graphic image is combined on a non-combined image. For example, a combined image may be displayed in which a graphic image is combined on an HDR image. For example, a graphic image refers to a graphical user interface (GUI) image of a mouse cursor, a menu, or the like that is generated in accordance with a user operation performed on a display apparatus or a PC. A user operation is, for example, a user operation for editing an HDR image.
However, in conventional art, images with a narrower dynamic range than the dynamic range of HDR images are used as graphic images. Therefore, when a combined image is displayed using an HDR monitor, brightness of a periphery of the graphic image may be inadvertently increased in comparison to the graphic image. As a result, the dazzle of the periphery of the graphic image may cause a decline in visibility of the graphic image.
In addition, as the graphic image, an image with a set transparency may sometimes be used. In other words, a graphic image that enables a transmission of a non-combined image at a set transparency may sometimes be used. Specifically, there is a technique in which a pixel value of a non-combined image and a pixel value of a graphic image are weighted at a set weight and then composited and the weighted and composited value is used as a pixel value of a combined image (Japanese Patent Application Laid-open No. 2003-162275).
However, even when the technique described in Japanese Patent Application Laid-open No. 2003-162275 is used, the brightness of the periphery of a graphic image may end up being higher than the graphic image. As a result, the dazzle of the periphery of the graphic image may cause a decline in visibility of the graphic image.
In addition, when using the technique described in Japanese Patent Application Laid-open No. 2003-162275, since a high-brightness pixel value of an HDR image and a pixel value of a graphic image are weighted and composited, a high-brightness pixel value may be produced as a pixel value after weighted composition. In other words, the brightness of the graphic image may be increased in the combined image. As a result, the dazzle of the graphic image may cause a decline in visibility of the graphic image.
The dazzle that makes an object less visible is referred to as a “glare”. The higher the intensity of light irradiating an object, the greater the glare and the greater the decline in visibility of the object. Therefore, the higher the brightness of a graphic image or a periphery thereof, the greater the decline in visibility of the graphic image. In addition, the visibility of an object also varies in accordance with a solid angle between a line of sight of a person and a light source (a light source irradiating the object). For example, the closer the line of sight of a person is to a light-emitting direction of a light source, the greater the glare and the greater the decline in visibility of the object. Therefore, when the brightness of a graphic image or a periphery thereof is high, the decline in visibility of the graphic image increases in comparison to a case where brightness of a distant position from the graphic image is high.